A ProLogium lithium ceramic cell shown in cross-section. Official press image supplied by ProLogium.

Mercedes-Benz gets priority access to ProLogium Gen4 cells

Mercedes-Benz and Taiwan-based ProLogium signed a joint testing agreement on 24 September 2026 that gives the German carmaker priority access to Gen4 lithium ceramic cells. The companies have not named a production vehicle, battery capacity, vehicle range or launch date.

The cells will undergo electrical, thermal and safety testing at Mercedes-Benz facilities and specialised external institutes. The purpose is to determine whether the technology is suitable for potential future vehicles. That wording matters: this is a cell-evaluation programme, not confirmation that a solid-state Mercedes has been approved for sale.

What Mercedes-Benz will evaluate

Electrical testing can establish charge and discharge behaviour, power delivery, resistance and capacity retention over repeated cycles. Thermal work examines performance under load and at different temperatures. Safety testing is needed to understand how the cell responds to abnormal conditions and whether its protective mechanisms remain effective in an automotive format.

ProLogium describes Gen4 as a platform using a non-flammable inorganic electrolyte, ceramic separator technology and a proprietary active-safety mechanism. The supplier says the architecture is intended to support high energy density, fast charging, high power and low-temperature operation while remaining scalable and cost-competitive.

Those are supplier claims and design objectives, not Mercedes-Benz test results. The agreement exists so that the carmaker and outside laboratories can measure the technology against vehicle requirements. No raw test data accompanied the announcement, and the partners did not disclose cycle life, cell size, pack pressure requirements or a vehicle-level charging curve.

Gen4 is not the recently announced Gen3.5 cell

On 2 September 2026, ProLogium separately announced production of a 185.4 Ah Gen3.5 lithium ceramic cell at its Taoke facility in Taiwan. A TÜV report cited by the company measured 381 Wh/kg gravimetric energy density and 903 Wh/l volumetric energy density. UL Solutions also tested the cell under China's GB/T 43568-2026 methodology: after six hours in a vacuum at 120°C, it lost less than 0.05% of its mass, below the standard's 0.5% threshold for all-solid-state classification.

Those numbers describe Gen3.5, not the Gen4 cells entering Mercedes-Benz evaluation. The generations share ProLogium's Logithium cell architecture and related manufacturing platform, but Gen4 introduces the supplier's superfluidised all-inorganic electrolyte system. Assigning the 381 Wh/kg and 903 Wh/l measurements to the new Mercedes programme would therefore combine two different products.

ProLogium has published ambitious fast-charging and energy-density material for Gen4 elsewhere. The joint announcement, however, does not provide an automotive test protocol, initial and final state of charge, cell temperature, charging power or pack size. Without those conditions, a charging-time claim cannot be compared fairly with a current production EV.

The relationship dates back to 2016

The two companies say they have worked on EV-cell testing since 2016. In January 2022, Mercedes-Benz and ProLogium announced a technology-cooperation agreement, a Mercedes investment in the high double-digit millions of euros and a seat for the carmaker on ProLogium's board.

That 2022 release expected jointly developed test vehicles in the following years and referred to milestones for possible integration into passenger vehicles in the second half of the decade. The partners have since validated lithium ceramic cells in pouch and prismatic formats as well as ProLogium's bipolar technology. The 2026 agreement narrows the immediate task to Gen4 testing, but does not say that the earlier vehicle-integration milestone has been completed.

Mercedes-Benz is also running a separate solid-state programme with Factorial Energy. In February 2025, it began road testing an EQS-based prototype using Factorial lithium-metal cells. Mercedes said that demonstrator's battery could provide up to 25% more range than a corresponding standard EQS battery of comparable weight and size. It is a different chemistry and supplier programme, so its range result cannot be attributed to ProLogium Gen4.

The two parallel projects show why the supplier name is important when reading solid-state announcements. “Solid-state” covers different electrolyte, separator and anode designs, each with its own packaging, operating conditions and manufacturing route.

Production in Taiwan, construction in France

ProLogium says its Taoke gigafactory in Taoyuan has completed GWh-scale manufacturing validation and can support C-sample cells, demonstrator programmes and future commercial production. C-samples are a development milestone; they are not proof that a battery has been homologated in a customer vehicle or ordered at mass-market volume.

The company broke ground on a second gigafactory in Dunkirk, France, in February 2026. Its first phase is designed to reach 4 GWh of annual capacity progressively by 2030. The entire site has a planned maximum capacity of up to 44 GWh. The larger number is the intended upper scale of the project, not current output.

ProLogium also operates a European research centre at Paris-Saclay. If cell qualification and industrialisation proceed as planned, the French factory could supply European vehicle programmes without importing every cell from Taiwan. The testing agreement does not state that Mercedes-Benz has reserved Dunkirk capacity or committed to a purchase volume.

What the agreement does — and does not — mean

For a cell to move from priority testing to a showroom vehicle, Mercedes-Benz would still need to design and validate the module or pack, thermal system, battery-management electronics, crash protection and production process. Durability, repeatable quality and cost also have to work at automotive scale.

The next useful evidence would be published test results, a Gen4 demonstrator vehicle or a named production programme. Until one of those appears, the confirmed development is limited but clear: Mercedes-Benz has secured an early position to test ProLogium's latest cells, and ProLogium must now prove that its laboratory and manufacturing claims translate into a complete vehicle battery.

Sources